1. Field of the Invention
The present invention relates to a liquid crystal display apparatus, and more specifically, to a liquid crystal display apparatus provided with a light emitting layer.
2. Description of the Prior Art
In recent years, liquid crystal display apparatuses have frequently been used as information displaying means for use in various apparatuses such as word processors, television receivers and personal computers. Liquid crystal display apparatuses are designed to obtain a desired display pattern by using an optical change of liquid crystal caused by applying a voltage between two opposite electrodes of a liquid crystal panel made by enclosing liquid crystal between two transparent plates each including a transparent electrode.
However, since liquid crystal itself emits no light, to recognize the display pattern, it is necessary to use external light or to provide some kind of light source. As methods to directly view the display pattern of the liquid crystal panel, a reflection type and a transmission type are known. In the reflection type, a reflecting plate is provided on the back surface of the liquid crystal panel, and external light incident on the liquid crystal panel is reflected by the reflecting plate. In the transmission type, a light source is provided on the back surface of the liquid crystal panel, and light from the light source is transmitted by the liquid crystal panel.
A reflection-type liquid crystal display apparatus, which requires no light source in the apparatus, has advantages that the power consumption is very low and that the size and weight of the apparatus can be reduced. However, since external light is used, it is difficult to view the display pattern at dark places.
With a transmission-type liquid crystal display apparatus in which light is supplied from the light source, a bright display pattern can always be viewed at any places. However, since the light source is incorporated, the size of the apparatus increases, so that it is difficult to mount it in a small-size electronic apparatus. In addition, the power consumption increases. As the back light source provided on the back surface of the liquid crystal panel, a fluorescent lamp and an electroluminescence (EL) light source are widely used.
Referring to FIG. 1, there is shown a liquid crystal display apparatus using a fluorescent lamp as the back light source. Within a fixing frame member 1 having a display window at its upper surface, a liquid crystal panel 2, a plate-form back light 5 and a back cover plate 7 are provided. The liquid crystal panel 2 includes two transparent plates 2a and 2b each having on its inner surface a transparent electrode comprising indium tin oxide (ITO). Liquid crystal is enclosed between the transparent plates 2a and 2b. In the periphery of the liquid crystal panel 2, circuit boards 4a and 4b each having an electronic part for driving the liquid crystal are arranged. The electronic parts are mounted on flexible boards 3a and 3b, respectively, by the tape automated bonding (TAB) method. The end portions of the flexible boards 3a and 3b are each connected to an electrode pattern at a periphery of the liquid crystal panel 2. The back light 5 includes fluorescent lamps 5b and 5c arranged below the circuit boards 4a and 4b and a transparent plate 5a arranged to connected the fluorescent lamps 5b and 5c and having a light intercepting plate. Cushioning materials 6a and 6b are provided between the under surface of the liquid crystal panel 2 and the under surfaces of the circuit boards 4a and 4b, and the back light 5, and cushioning materials 8a and 8b are provided between the back light 5 and the back cover plate 7. Thus, the back light 5 is supported.
In the above-described arrangement, a voltage is applied to the electrodes of the liquid crystal panel 2 by the electronic parts mounted on the circuit boards 4a and 4b, so that a display pattern is formed on the liquid crystal panel 2. The light from the fluorescent lamps 5b and 5c is directed by the transparent plate 5a to irradiate the back surface of the liquid crystal panel 2, and a part of the light is transmitted by the liquid crystal panel 2 in accordance with the display pattern. The display pattern is viewed by the eye by observing the transmitted light.
A liquid crystal display apparatus using as the back light an EL light source using light emission caused by applying an electrical field to a substance is described, for example, in Japanese Laid-open Patent Application No. H3-282419. In this prior art, as shown in FIG. 2, an EL back light panel 11 supported by a guide 10 at its end is arranged between a liquid crystal panel 2 and a circuit board 4 which are fixed to a fixing frame member 1. The liquid crystal panel 2 is connected to the circuit board 4 by a conductive film 9. A voltage is applied to the electrodes by an electronic part (not shown) for driving the liquid crystal mounted on the circuit board 4, so that a display pattern is formed on the liquid crystal panel 2. The EL back light panel 11 emits fluorescence by being supplied with an electrical field by a non-illustrated power source, and the light is transmitted by the liquid crystal panel 2, so that a display pattern is viewed.
However, in either of the above-described transmission-type liquid crystal display apparatuses, a power source and a driving circuit to cause the fluorescent lamp and the EL back light source to emit light are necessary, which is an obstacle to the reduction in size and weight of the display apparatus and the apparatus in which the display apparatus is to be incorporated. In addition, in the liquid crystal display apparatus of FIG. 1 using the fluorescent lamp as the light source, since the circuit board for driving the liquid crystal panel 1 is arranged in the periphery of the liquid crystal panel 1, a frame member area B is large compared to an effective display area A.
In the liquid crystal display apparatus using the EL back light source, due to the electrical field applied to the EL back light source, static electricity may be generated on the liquid crystal panel and noise may be generated at the electronic part. These lead to a mis-operation of the liquid crystal display apparatus. For this reason, in the liquid crystal display apparatus of FIG. 2, it is necessary that a distance L1 between the EL back light source 11 and the liquid crystal panel 2 and a distance L2 between the EL back light source 11 and the circuit board 3 should be sufficiently large, so that the thickness of the apparatus increases.